This invention relates to inorganic particulate fillers useful in the production of substantially fireproof foamed polymeric products and other materials. More particularly, the invention relates to the production of polymeric materials which are self fire-extinguishing, low smoking, and substantially non-dripping, even when exposed directly to a flame for substantial periods of time, and which retain acceptable mechanical properties.
Foamed polymeric materials are produced from a variety of thermoplastic, thermosetting, and other resins using conventional techniques involving expansion of various thermoplastic polymers or formation of polymers in the presence of a blowing agent. Blowing agents serve to produce a multiplicity of open or closed cells within the polymer structure, resulting in expanded, light weight materials having significant and diverse commercial uses. The patent and other literature is replete with methods for producing foamed polymers having various chemical and physical properties. Currently, rigid and flexible foamed plastic materials are available commercially, essentially world-wide, which have various densities and open or closed-cell structures. The foams are fabricated from a great variety of resins or prepolymer mixtures. These materials are used for cushioning, thermal and electrical insulation, and structural applications.
Polyurethane foams are perhaps the most commercially successful as measured on a production volume basis. Generally, polyurethanes are produced by reaction of a polyisocyanate and a polyol, i.e., organic structures having at least two isocyanate or alcohol groups, typically in the presence of a catalyst, and in the presence of a blowing agent. Flexible polyurethane foams are widely used in the production of matresses, cushions, and other soft-furnishings, protective packaging, carpet underlay, fabric backing, and in automobile and aircraft seats. Polyurethanes also are used to produce rigid structural elements which are inert, thermally insulating, and producible in a variety of useful shapes.
It has long been recognized that foam plastic materials are flammable and present a significant fire hazard. Upon exposure to fire or high temperatures, most foam plastics, because of their cellular structure, high organic content, and large surface area, decompose and burn rapidly emitting abundant smoke and producing flowable, flame supporting drips which serve to spread the fire. Once ignited, foam plastics not specifically designed to be fire resistant are rapidly and completely consumed. Because foam materials often are used in quantity in enclosed living space and in vehicles, the industry has long sought fireproofing methods so as to reduce or eliminate the fire hazard.
A review of the literature suggests three basic approaches. Perhaps least versatile is the technology disclosed, for example, in U.S. Pat. No. 4,349,494, broadly involving the concept of protecting a foam plastic material within a sheath or coating of nonflammable or fire resistant material. A second approach involves chemical engineering of the polymer or monomers from which the foam is made so as to decrease the flammability of the solid phase of the foam structure itself. This approach is exemplified by the many disclosures involving the use of halogenated organic polymers. The third general approach involves mixing fire retardant or fire resistant filler materials within the continuous phase of the foam's structure. Upon exposure to heat above the foam's ignition temperature or to flame, the fillers expell nonflammable gases locally, or form a semi-continuous layer on the surface exposed to the flame, both of which have the effect of limiting oxygen transport to the organic fuel. While the latter two methods both have significant beneficial fire retardant effects, neither approach has heretofore yielded foams which meet the emerging international fire resistance standards for foamed plastics.
For a general discussion for the state of the art of foam plastic fire retardant technology, see, for example, HANDBOOK OF PLASTICS FLAMMABILITY AND COMBUSTION TOXICOLOGY (A. H. Landrock, Noyes Publications, 1983) chapter 4, "Fire Retardants"; Alumina Trihydrate as a Flame Retardant for Polyurethane Foams, JOURNAL OF CELLULAR PLASTICS, July/August 1981, page 220; Alumina Hydrate as a Flame-Retardant Filler for Thermoplastics, I. Sobolev et al, 31st SPE ANTEC, Montreal, May 7, 1973; Fire and Cellular Polymers, J. M. Buist et al, Elsevier Applied Science, 1986; and Flammability Handbook for Plastics, third edition, C. J. Hilado, Technomic Publishing Co., 1982, particularly, chapter 5, "Prevention, Inhibition and Extinguishment".
U.S. patents disclosing compositions for inclusion in foamed polymers to impart fire retardant or fire resistant properties include Schmittmann et al, U.S. Pat. Nos. 4,438,028; Hicks, 4,504,603; Priest, 4,224,374; Fulmer et al, 4,237,182; Kumasaka et al, 3,737,400; Brown et al, 4,246,360; Wright, 3,719,614; Wortmann et al, 4,097,400; Rigge et al, 4,216,130; Pcolinsky, Jr., 4,317,889; Szabat, 4,546,117; Rodish, 4,182,799; Otten, 4,273,881; Geppert et al, 3,874,889; Yakuta et al, 4,066,579; Gardner, 4,315,075; Hart et al, 4,190,696; Anorga et al, 3,909,464; and Cenker et al, 4,150,207. These patents disclose various inorganic additives used alone, in combination with each other, or in combination with particular halogen-derivitized polymers, char forming agents, and other substances which decrease foam plastic flammability. However, none of the disclosed formulations are believed to impart adequate fire resistance to foamed polymers.
The chemistry of ignition, fire propagation, and fire retardancy in foamed polymers is extremely complex and generally not well understood. Reducing smoke generation, the tendency of burning foam polymers to drip and run, and the fire propagating properties of foams exposed to flame are goals extremely difficult to obtain in combination, particularly with respect to nonthermoplastic foams such as polyurethanes.The need for such materials has increased as the market expands and the volume of foamed materials used in enclosed spaces increases.
It is an object of this invention to provide compositions of matter useful as fillers in a variety of foamed and unexpanded plastic materials, paints, and other coating compositions which impart to the materials a level of fire resistance heretofore unknown in the art. Another object is to provide filler compositions readily adaptable for use in thermoplastic, thermosetting, and other types of foams which impart fireproofing properties at loading levels resulting in only moderate, acceptable reductions in the foam's mechanical properties. Another object is to produce various types of foamed polymeric materials characterized by relatively low smoke generation, substantially eliminated tendency to drip or flow while burning, and a self-extinguishing property. Another object is to provide flexible and rigid foams which may objectively be characterized as non-burning, that is, unable to sustain or spread fire even when directly exposed to a flame, e.g., from a blow torch. Another object is to provide fireproof rigid and flexible polyurethane foams. Yet another object is to provide inorganic compositions of matter which may be added to foam plastic and other polymeric formulations to reduce the fire hazard they present.
These and other objects and features of the invention will be apparent from the description and claims which follow.